The present invention relates to a hull capable of performance in a combination of speed and seakeeping heretofore found separately in displacement and planing hull types. The two qualities have always been difficult to combine because they depend on decidedly different hull forms.
The seakeeping characteristics of displacement hulls are well known. They are most evident in the classic lines of traditional sailing vessels with graceful curvature fore and aft to move easily under sail through the water and follow the waves. Those lines are little changed in the ocean-going ships of today, with their pointed bows, round bilges, rounded sterns, and amidships balance to ride as level as possible in meeting seas under all weather conditions.
More recently, hull speed has been increased by use of a very different hull form from that of displacement vessels, enabling such planing hulls to rise bodily towards the water's surface and move at higher speed because of less water resistance. Typically, planing hulls have sharp-cornered chines, flat bottom surfaces aft, and square transoms. For the sake of speed, they have given up some of the seakindly configuration of their predecessors, tending in a seaway to leap from the crest of each wave and to slam violently into the next.
The development of fast planing hulls began with the design of racing hydroplanes in the early 1900s, and they set the style for all speed boats with wide, flat planing surfaces aft. Morever, powerboats have been inclined to settle by the stern as they pick up speed; and that tendency is often aggravated into a bad squat as a fast boat rises up to plane. A typical planing hull then assumes an ungainly attitude, with its bow riding well up out of the water at high speed, an attitude safely maintained only in calm water.
Numerous inventions over the years have tried to correct the problem of poor planing trim, usually by adding some leveling or stabilizing device. For example, Weiland's U.S. Pat. No. 988,437, dated July 18, 1911, and Prosser's U.S. Pat. No. 1,075,726, dated Oct. 14, 1913, both attached something like water skis to either side of a small, narrow boat. More recent attempts to improve trim were in having slightly concave bottom lines aft to keep the stern up by deflecting passing water downward, as disclosed in the Burgess U.S. Pat. No. 2,185,430, dated Jan. 2, 1940, and the Troyer U.S. Pat. No. 2,342,707, dated Feb. 29, 1944.
The introduction of fiberglass boatbuilding in the 1950s boosted mass production of planing hulls by the use of molds to provide hulls in almost any shape or form. Since then, extruded panels, steps, and chine lips have become common in multiple horizontal surfaces added to the basic vee-bottom. In what has been popularly accepted as modern styling, the extra angles and curves seem to create an illusion of speed, but speed is actually reduced by the increase in wetted surface. Improvement in trim may be claimed or implied, but there has actually been little change in planing performance. Examples of such modern design in fiberglass planing hulls include those disclosed in the Becker U.S. Pat. No. 2,634,698, dated Apr. 14, 1953; the Canazzi U.S. Pat. No. 2,980,924, dated Apr. 25, 1961; and the Schoell U.S. Pat. No. 4,193,370, dated Mar. 18, 1980.
A significant improvement in planing hull design occurred in 1959 when the so-called "deep vee" for ocean racing put a definite dihedral or deadrise angle in a planing hull bottom. The change became popular and was widely copied as it greatly improved directional stability for open ocean operation. However, the improvement had little efect on planing aspect or trim and thus did not minimize slamming or pounding by the forward portion of the hull. The latest models are still characterized by hard chines, vee-bottoms, and broad transoms to carry maximum planing surfaces farthest aft; and planing hulls still ride on their afterbodies, being notoriously rough in any waves.
While there has been no fundamental change in planing hull lines to achieve a desirable minimum angle of trim, trim tabs are commonly installed at the transom to offset an extreme squat. Similar to the former use of wedge-shaped blocks under the transom to force the water down and push the stern up toward a more horizontal position, external contrivances like trim tabs have only a limited effect, as they function at some expense of economy or speed. Any such projections from the hull proper, whether in attachments or extrusions, will reduce speed by adding to wetted surface and parasitic drag. Reverse curves or warped planes have the same adverse effect by increasing the area of skin friction and distorting the free flow of water past the hull.
Riding trim is largely a matter of innate balance, something primarily in hull form not very well managed by simply adding to or changing hull surfaces. A slow and well balanced displacement vessel accepts sea conditions most agreeably without pounding or slamming; but a fast hull, riding on her after planes with a high bow, can only meet the waves with violent impact.